Thank you. I had studied optimization of performance through simulation by changing shield dimensions and noticed improvement in Q factor.

One helpful way is to employ simulation software. This way it is possible to choose one design, test it by running a simulation and then change the suitable parameters to obtain a better performance in the next simulation. These steps must be repeated untill the desired performance is obtained, and then it is ready to be fabricated. 

There are several parameters to be optimized to obtain a good Q factor. It ts very important that the impedance of the feed vias matches the impedance of the source and the load (usually 50 ohm) in order to get the maxim power transfer. The length of the ring must match an integer number of times of the wavelength related to the resonant frequency. The coupling gaps must be short enough to suitably feed the ring. Finally, the width of the ring is very important to obtain the desired frequency response, remember that a bigger width makes axial currents to appear, which are governated by Bessel functions.

Hope this was helpful.